The growth of a normal cell or of a virus in its host cell involves a complex pattern of gene expression in which individual genes or groups of genes are activated or repressed at appropriate times during growth. Studies of the growth of bacterial cells and of bacteriophages have provided an important model system for the study of how gene expression is regulated. Those studies suggest that regulation of transcription -DNA dependent synthesis of messenger RNA - is of major importance in the control of gene expression. We propose to continue our studies of the steps involved in enzymatic transcription by E. coli RNA polymerase. Specific goals will be (1) Isolation of E. coli core RNA polymerase free from trace contamination by sigma subunit. (2) Continued study on the steps in location and utilization of promoter and terminator sites in T7 and T3 DNAs by bacterial RNA polymerase holoenzymes employing quantitative electron microscopic analysis, filter binding and gel electrophoretic analysis of RNA transcripts. (3) Use of the T7 minor promoter system to study changes in transcriptional specificity of bacterial RNA polymerase including differences in different cellular forms of the enzyme, alterations due to phage infection and mutational lesions in the RNA polymerase protein.